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We study via molecular dynamics simulations the self-assembled structures formed by supracolloidal magnetic polymers (SMPs). These are small aggregates of magnetic colloidal particles with polymer-like structures that have been permanently stabilized by means of polymer crosslinking. Here we focus on the fundamental structural and magnetic properties of the self-assembled motifs formed by pairs of identical SMPs under different conditions. We observe that the minimum characteristic density at which the self-assembly of both SMPs into a single aggregate becomes dominant is signaled by a maximum in their net magnetization and radius of gyration.

In the present work we study via molecular dynamics simulations filaments of ring and linear shape. Filaments are made of magnetic nanoparticles, possessing a point dipole in their centres. Particles in filaments are crosslinked in a particular way, so that the deviation of the neighbouring dipoles from the head-to-tail orientation is penalised by the bond. We show how the conformation of a single chain and ring filament changes on cooling for different lengths. We also study filament pairs, by fixing filaments at a certain distance and analysing the impact of inter-filament interaction on the equilibrium configurations. Our study opens a perspective to investigate the dispersions of filaments, both theoretically and numerically, by using effective potentials.

In our earlier work (Steinbach et al., 2016 [1] ) we investigated a homogeneous system of magnetically capped colloidal particles that self-assembled via two structural patterns of different symmetry. The particles could form a compact, equilateral triangle with a three-fold rotational symmetry and zero dipole moment and a staggered chain with mirror symmetry with a net magnetisation perpendicular to the chain. The system exhibited a bistability already in clusters of three particles. Based on observations of a real magnetic particles system, analytical calculations and molecular dynamics simulations, it has been shown that the bistability is a result of an anisotropic magnetisation distribution with rotational symmetry inside the particles. The present study is a logical extension of the above research and forms a preparatory stage for the study of a self-assembly of such magnetic particles under the influence of an external magnetic field. Since the magnetic field is only an additive contribution to the total ground state energy, we can study the interparticle interaction energies of candidate ground state structures based on the field-free terms.

Using Molecular Dynamics computer simulations, we study how an applied magnetic field influences the shape, integrity and internal structure of clusters formed by Stockmayer supracolloidal magnetic polymers (SMPs). We consider SMPs of four different topologies: chain-, Y-, X- and ring-like ones. We find that the highest macroscopic deformation and the strongest monomer rearrangements from a liquid to a local hexatic order is observed for clusters formed by chain-like SMPs. The highest magnetic susceptibility, however, is exhibited by the clusters composed of Y- and X-like SMPs. Clusters formed by ring-like SMPs are basically not affected by the field strengths considered here. It is worth mentioning that those fields are sufficient to cause the dissociation of the clusters formed by other topologies of SMPs.

Supracolloidal magnetic polymers (SMPs) are structures made by crosslinking magnetic particles. In this work, using Langevin dynamics simulations, we study the zero-field magnetic properties of clusters formed in suspensions of SMPs with different topologies -- chains, rings, X and Y -- that interact via Stockmayer potential. We find that the presence of central attraction, resulting in the formation of large compact clusters, leads to a dramatic decrease of the suspension initial susceptibility, independently from SMP topology. However, the largest decrease corresponds to chain-like SMPs with strongly interacting particles. This is due to the higher rotational degrees of freedom of SMPs with such topology, which allows the particles to reorganise themselves inside the clusters in such a way that their magnetic moments form energetically advantageous vortex structures with negligible net magnetic moments., Comment: International Conference on Magnetic Fluids - ICMF 2019

We present a comparative study of the anisometric and anisotropic magnetic colloids at low temperatures. As examples we choose the ellipsoidal and cubic magnetic colloids to illustrate the influence of the shape (particle anisometry) on the ground state structures. To scrutinise the influence of the internal particle anisotropy we address particles with dipoles shifted out from the centre of mass. Of the latter, we distinguish between two types: the first type has a dipole moment pointing radially outwards; the other has a dipole pointing perpendicular to the radius along which it is shifted.